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Drug makers would love nothing better than to develop effective anti-obesity medications, but it is proving very difficult to manipulate the body’s powerful weight-control systems without serious side effects.

Only three FDA-approved drugs are on the market:

 Meridia: One of two drugs approved for long-term use, Meridia is an amphetamine-like compound that boosts brain levels of two neurotransmitters  serotonin and noradrenaline. It lessens hunger pangs and creates a feeling of fullness, resulting in a 5 to 10 percent weight loss.

But it also increases blood pressure and is the subject of a class-action lawsuit and an FDA investigation. Worldwide, 34 people have died while taking the drug, several from heart problems; manufacturer Abbott Laboratories says the death rate among the 8.5 million people who have taken Meridia is much lower than normal for an obese population.

 Xenical: Also approved for long-term use, it reduces fat absorption by blocking certain enzymes. People who take Xenical while dieting lose 2 to 3 percent more weight than through diet alone, but many gain it back. Severe diarrhea is a common side effect.

 Phentermine: The phen portion of the infamous combination drug fen-phen, or Redux. “Fen” was banned in 1997 after reports of death and heart problems. Phentermine, which suppresses appetite, is approved only for short-term use.

Many other drugs are in the pipeline, including:

 Cannabinoid receptor inhibitors: These compounds block the brain receptors responsible for “the munchies” associated with marijuana use. The hope is that the drugs will suppress the urge to eat.

 Axokine: Originally developed to treat Lou Gehrig’s disease, this synthetic hormone activates brain cells that decrease appetite. In continuing trials, obese patients lost 4 percent of their body weight and kept it off for up to a year.